condensing boilers

[gazz]

Do condensing boilers condense all the time, and if so do they always emit a plume of vapour whilst they are doing so??

We have finaly got our boiler replaced in the bungalow we're renting, it died on the 22nd of feb this year, someone was sent to look at it, dead main board, uneconomical to repair, quoted for a top of the range workie bosch jobbie at 1600 squids, so i wasnt surprised when they never came back to fit it,

another plumber was booked to come and quote, phoned us up and arranged a time and date, but never turned up, and we had nowt but excuses from the managment company, in june they told us 'it's getting warmer now, so you dont really need heating do you' yes i suppose we could keep wrapping up in blankets and heating just one room with an electric heater, but we would like to have hot water available on tap, instead of from the kettle, which can't be used for the shower which is a mains hot and cold fed off the combi.

complained, got CAB involved, a soliciters letter sent, got nowhere, was ready to find somehwere else to live.... which isnt that easy, finding a landlord who will accept LHB, a dog and 4 fancy rats isnt easy, took us 5 months to find this place.

Anyway, out of the blue we got a letter from another managment company telling us they had taken over from the old un, so i reported the boiler, someone came out the next day and confirmed it was beyone economical repair, and arranged for a new un to be fitted, week later it happened, plumber bods who came were the same uns who were to have come back in may, he'd recieved an e-mail the day after he'd phoned us telling him to cancel the job and not to tell us!!!

apparantly they are owed the best part of 10 grand from the old managment company, and to top it all, our landlord didnt even know our boiler was broken, old managment company never told him, apparantly there was some fiddle going on, this plumber has fitted new boilers to about 25 other properties owned by our landlord, they all had the same, managment company werent telling the landlord and giving excuses for not sorting it... of course they would never tell us who the actual landlord was... data protection and all that they would say.

we were told who the landlord was by the new managment company straight away, they say it's a legal right for us to know who actually owns the property, even if a managment company is used,

Anyway, we now have a ravenheat 85T 28KW combi, they had to put it in a new location as they only had a horizontal flue kit for it, and they had come down from liverpool, but tht free's up the rest of the old airing cupboard nicely, would be great if we could remove the wall as it is built into the kitchen,

So took them quite a bit longer than they expected, but it's all in and working, we have a warm house at last and can use the house's shower again (had been using the shower in my motorhome, which usually stays at my parents house, if we didnt have that we'd have been well and truly stuffed)

anyway, when the boiler first starts up, after a few seconds of the burner coming on, you get a plume of vapour from the exhaust, which i know is normal, this plume will keep being emited for about 10 minutes, then it'll stop, now i dunno if that's cos the boiler is going out of condensing mode, or it was like petrol cars exhaust on a cold morning, lots of vapour untill the system has warmed up.

the boiler's controlls are set on the 'super efficiant condensing mode' positions, and the burner has been on high for a good hour... having to heat the house up from scratch, it's now modulating down as we're aproaching the set temperature on my wirless room stat,

we have no TRV's, and ATM all rad valves are fully open,

oh, anyone want to buy any parts for a halstead finest gold combi boiler, had a brand new fan in november last year, so only been used for 3 months, got everything except the main board as that's knacked.

[YAPH]

Oh, dear: no-expense-spared job then :-/

In this relatively warm weather that's not too surprising: as the readiators warm up and the water returning to the boiler gets warmer it'll condense less, and the proportion of water vapour in the flue gases will drop to the point that they no longer condense further in the outside air. They'll still be condensing in the boiler itself. In colder weather the small amount of water vapour that escapes in the flue gas will be more prone to condense as it hits colder outside temperatures (same way the water vapour in your breath condenses in cold weather).

Not to standards: controls should by law (building regs) have been upgraded to include at least some TRVs

[Dave Liquorice]

Hum, so with a fixed amount of water vapour in the flue gases from the burner less is condensed out and the amount of water vapour in the exit gases also falls?

Whether you get a visible plume or not depends mainly on the exit gas temperature and the external temperature. Does the cooling of the exit gases by the colder external air bring them below the dew point. The more condesation you get in the boiler the cooler the exit gases will be, thus more likely to get a visible plume as they don't have to be cooled so far to get below the dew point.

Do the building regs have any force of law? Also I didn't think the building regs specified TRVs. Only some means of stopping the boiler short cycling once the demand has been met.

[Neil]

Well as its a Ravenheat I expect you'll be seeing plenty more of the plumbers !!

[gazz]

well the landlord has had to pay for over 30 of his houses to have new boilers at the same time due to the last managment company for some reason not telling him, but i'm not fussed, it's a damn sight better than the halstead thing that was there before,

[John Rumm]

The are generally more efficient all the time due to larger heat exchangers and other technological improvements (forced induction, no pilot lights etc), but don't necessarily condense as effectively all the time. They tend to get more effective with lower return temperatures - with an change in the rate of improvement as the return falls below 56 =

57 ish (the dew point of the exhaust vapour).

Note also that many combis don't actually condense much in hot water mode.

Its efficiency will have fallen a bit as the return temp rises. This is basically as there is not really enough heating load in the relatively mild weather. The boiler will tend to modulate down to maintain condensing efficiency as best it can in the circumstances.

Yup, sounds like its doing what you would expect.

[YAPH]

IANAL but AIUI building regs do have force of law.

Somewhere they specify that controls must be improved when a boiler is replaced, and I'm pretty sure they do specify at least some TRVs - as well as boiler interlock.

[Harry Bloomfield]

It happens that YAPH formulated :

I wasn't aware of that, could you provide a reference?

[YAPH]

ADL1 35 b. refers to controls meeting Domestic Heating Compliance Guide, which seems - in a contorted sort of way[1] - to call for them.

[1] not least in the sense that the relevant part of the PDF is oriented sideways so you get a crick in your neck trying to read it :-(

[John Rumm]

In one of the tables: